I just sold my Spacekap Diablo build, for no reason due to the Diablo. It's truly awesome and it makes every other truck camper on the market seem like a rattly piece of junk. There's no need to pop it up, it's relatively aerodynamic, and the full-size van-style doors are convenient for loading cargo.
I even ricocheted off a guardrail at 35 mph with the Diablo on and it never budged. That impact broke my outer tie rod, bent my inner, and likely damaged a ball joint and half-sheared off the front recovery point for reference. I was able to drive away from the accident by using a ski strap to connect the tie rod back to the knuckle, but that's another story. But the Diablo is amazing and should last years and years.
For what it's worth, I never insulated mine and was fine. The fiberglass works great and it gave a nice open feeling to the build. Plus, insulation unless done perfect = mold and disgustingness.
With the volume and surface area of the build, plus the gigantic uninsulated doors -- the same amount of insulation won't be as effective as compared to say a larger traditional truck camper or a trailer. So it'd need to be fairly thick if you want high performance (like the Loki). In my case I just put more heaters rather than insulation which I used when it was below 20-degrees. Above 20-degrees a single 2kw diesel heater on max was perfect.
